In an example of an image forming apparatus such as a laser printer, a drum cartridge holding a photosensitive drum is removably provided in the apparatus body, and a developing cartridge holding a developing roller is mounted to the drum cartridge.
When the developing cartridge is mounted to the drum cartridge, the developing roller is pressed against the surface of the photosensitive drum. When the developing roller is pressed against the surface of the photosensitive drum, since the pressed part of the developing roller moves in the same direction as the surface of the photosensitive drum, the developing roller is rotated in a direction reverse to the rotation direction of the photosensitive drum. With the rotation of the photosensitive drum and the developing roller, toner is supplied from the developing roller to the surface of the drum body, and an electrostatic latent image formed on the surface of the drum body is developed to a toner image. In addition, a supply roller is rotatably kept in the developing cartridge. With the rotation of the supply roller, the toner in the developing cartridge is supplied to the surface of the developing roller.
A coupling member and a gear array are arranged at one of the sides of the developing cartridge. Driving force from a motor provided in the apparatus body is input to the coupling member. Then, since the driving force is transferred from the coupling member to the developing roller and the supply roller via the gear array, the developing roller and the supply roller are driven and rotated (see, for example, No. 2001-249542).
The gear array includes a plurality of gears, that is, a developing roller gear and a supply roller gear which are directly connected to the rotation axes of the developing roller and the supply roller, respectively, multiple intermediate gears for transferring the driving force input to the coupling member to the developing roller gear and supply roller gear, and the like. Therefore, if these gears are not arranged in suitable positions, the area occupied by the gears of the developing cartridge when viewed from the shaft direction of the developing roller becomes larger, and thus the miniaturization of the developing cartridge is difficult.